1. Field of the Invention
The present invention is related to accessories for vehicles and, more specifically without limitation, to an apparatus for towing a vehicle behind another vehicle.
2. Discussion of the Related Art
There is an ever-increasing need to be able to tow a driverless vehicle behind another vehicle. One common situation where this need arises occurs for persons traveling in a motorhome. Most motorhomes are too large to conveniently visit many sites of interest near an overnight stop-over. As a result, many motorhome users tow a small automobile behind their motorhome so the small automobile can be used for local transportation after the motorhome has been parked.
Various devices are used for towing a vehicle, sometimes referred to herein as a towed vehicle, behind another vehicle, sometimes referred to herein as a towing vehicle. One such device is commonly referred to as a dolly. A dolly is generally a two-wheeled vehicle with a tongue that connects to a trailer hitch, such as a ball-type hitch, fixedly connected to the rear of the towing vehicle. To tow a vehicle with the dolly, the vehicle to be towed is driven up behind the dolly and, by use of a small ramp-like arrangement, onto the dolly so the front wheels of the towed vehicle are supported by the dolly. The front wheels are then securely clamped to the dolly, such as with chains and turnbuckles, or other suitable clamping arrangement. When the towing vehicle is driven forward, the dolly follows the towing vehicle by virtue of the connection between the dolly and the trailer hitch of the towing vehicle, and the towed vehicle follows the dolly by virtue of the front wheels of the towed vehicle being supported by and clamped to the dolly.
A major drawback with the use of a dolly occurs when it becomes necessary to back up the tandem assemblage consisting of the towing vehicle connected to the dolly connected to the towed vehicle. The towing vehicle has a first set of wheels mounted on a front axle and a second set of wheels mounted on a rear axle. The dolly has a third set of wheels mounted on an axle, which constitutes a third axle spaced rearwardly from the two axles of the towing vehicle. The towed vehicle has a fourth set of wheels mounted on its rear axle, which constitutes a fourth axle spaced further rearwardly from the two axles of the towing vehicle and from the axle of the dolly. To operatively and simultaneously manipulate those four axles, each having a pair of wheels in contact with the ground therebeneath, such as when the tandem assemblage needs to be backed up, is a very difficult task even for an experienced driver. Of course, the towed vehicle could be unchained and unloaded from the dolly and individually driven out of the way, the dolly disconnected from the towing vehicle and physically placed out of the way, and the towing vehicle could then be backed up as needed. Obviously, such extra time and effort to simply back up the towing vehicle would be bothersome and aggravating, to say the least.
Another device that is commonly used to tow a driverless vehicle behind another vehicle is a tow bar. Tow bars are readily available in many different forms. Tow bars usually have either a socket at the forward end thereof for connecting to a ball-type hitch fixedly connected to the rear of the towing vehicle, or a square-shaped forwardly-extending tube for connecting to a conventional receiver hitch fixedly connected to the rear of the towing vehicle. In addition, tow bars usually have two towbar arms extending rearwardly to connect to the front end of a towed vehicle to thereby form a triangularly-shaped arrangement between the two towbar arms and the front end of the towed vehicle.
One such tow bar is disclosed in U.S. Pat. No. RE35,482 issued Mar. 25, 1997 to Andrew B. Johnson. The Johnson tow bar includes a forwardly-extending hitch tube for connecting to a conventional receiver hitch of a towing vehicle. A roll axis is defined by a fore-to-aft oriented pin pivotally connecting a rearwardly-directed yoke to a plate attached to the hitch tube. A pivot block, spaced rearwardly from the fore-to-aft oriented pin, has a horizontally-oriented throughbore oriented perpendicularly to the fore-to-aft oriented pin. A pitch axis is defined by a pin passing through the horizontally-oriented throughbore of the pivot block, which pivotally connects the pivot block to the yoke. The pivot block also has a vertical-oriented throughbore spaced rearwardly from the horizontal-oriented throughbore of the pivot block. A yaw axis is defined by a bolt passing through the vertically-oriented throughbore of the pivot block, which pivotally connects the pivot block to the forward ends of a pair of towbar arms. The rear end of each towbar arm includes a pivot arm for swinging around rearwardly to connect to a towed vehicle, or for swinging around forwardly to lock alongside the respective towbar arm for storage purposes. The Johnson tow bar can be pivoted upwardly about the horizontally-oriented pin through the pivot block for storage on the rear of the towing vehicle.
One problem with the Johnson tow bar is the plurality of moving parts thereof. Each of those moving parts are operatively subjected to substantial wear and abuse and therefore failure during use, namely, the fore-to-aft oriented pin, which is subjected to constant relative movement between the yoke and the plate attached to the hitch tube; the horizontally-oriented pin, which is subjected to constant relative movement between the pivot block and the yoke; and the vertically-oriented pin, which is subjected to constant relative movement between the towbar arms and the pivot block.
Another problem with the Johnson tow bar is the spaced-apart configuration of the various articulation axes thereof; more specifically, accommodation of roll, pitch and yaw movements between the towing vehicle and the towed vehicle are confined to separately-defined and spaced-apart axes: the fore-to-aft oriented pin through the rearwardly-directed yoke for roll movements, the horizontally-oriented pin through the rearwardly-directed yoke and the pivot block for pitch movements, and the vertically-oriented pin through the pivot block and the forward ends of the towbar arms for yaw movements. The cause for concern in regard to the spaced-apart structuring of the articulation axes of the Johnson tow bar arises from moments that are operatively created in the tow bar, which moments can only be countered internally within the tow bar by pitting one part of the tow bar against another part of the tow bar. Moments which must be countered internally within the tow bar increase wear and tear of those tow bar parts and, as a result, decrease the meantime before failure of the tow bar. More specifically, in the structure of the Johnson tow bar, the yaw axis is spaced rearwardly from the pitch axis which, in turn, is spaced rearwardly from the roll axis which, in turn, is spaced vertically from the fore-to-aft axis of the receiver hitch.
Various force components are imposed by the towed vehicle on the vertical pin through the pivot block, the yaw axis, by virtue of the towed vehicle being connected to the vertically-oriented pin by the towbar arms. For example, in any turning situation where the towed vehicle is not lined up rearwardly from the towing vehicle, the towed vehicle causes the towbar arms to impose a horizontal, transverse force component on the vertically-oriented pin through the pivot block. Although the yaw axis at that vertically-oriented pin of the Johnson tow bar can accommodate the transverse force components imposed thereon by the towed vehicle and the towbar arms, those transverse force components are, in turn, imposed on the vertically-oriented pin through the pivot block, and there is no other structure spaced forwardly therefrom that can provide another yaw axis to accommodate the transverse force components imposed on the vertically-oriented pin. The same reasoning applies whether the transverse force components are to the left or to the right—in other words, all turning situations.
Similarly, in any operative situation where the towing vehicle enters an upgrade or a downgrade before the towed vehicle enters that grade change or the wheels of the towing vehicle are momentarily supported on a plane that is at a different elevation than the plane supporting the wheels of the towed vehicle, the towed vehicle causes the towbar arms to impose a vertical force component on the vertically-oriented pin through the pivot block, which vertical force component is transferred to and accommodated by the pitch axis at the horizontally-oriented pin through the pivot block. However, there is no other structure spaced forwardly from the horizontally-oriented pin through the pivot block that can provide another pitch axis to accommodate the vertical force components imposed on the horizontally-oriented pin through the pivot block. The same reasoning applies whether the vertical force components are upwardly or downwardly—in other words, all pitch situations.
Finally, at all operative times, the towed vehicle causes the towbar arms to impose fore-to-aft force components or aft-to-fore force components on the vertically-oriented pin through the pivot block, such as when the towing vehicle and towed vehicle are speeding up, slowing down, going up or down an incline, or just cruising. The fact that the fore-to-aft oriented pin through the rearwardly-directed yoke is not aligned with the fore-to-aft oriented axis of the receiver hitch of the towing vehicle, such constantly varying fore-to-aft force components imposed by the towed vehicle and the towbar arms, create moments that must be countered internally by the plate attached to the hitch tube and by the connection of the fore-to-aft oriented pin to that plate. The magnitude of the lever arm of that moment would be the spacing between the orifice through the rearwardly-directed yoke for the fore-to-aft oriented pin and the receiver hitch of the towing vehicle.
In addition to the moments created in the fore-to-aft pin and the plate connecting that pin to the hitch tube by fore-to-aft force components, other moments which the Johnson tow bar must internally oppose from force components imposed on the tow bar by the towed vehicle and the towbar arms can be described as follows:                (a) transverse force components create (i) moments in the pivot block with the magnitude of the lever arm thereof being determined by the spacing between the vertically-oriented and horizontally-oriented pins through the pivot block, (ii) moments in the rearwardly-directed yoke with the magnitude of the lever arm thereof being determined by the spacing between the vertically-oriented pin through the pivot block and the orifice through the rearwardly-directed yoke for the fore-to-aft oriented pin, and (iii) moments in the fore-to-aft oriented pin and the plate attached to the hitch tube with the magnitude of the lever arm thereof being determined by the spacing between the vertically-oriented pin through the pivot block and the hitch tube; and        (b) vertical force components create (i) moments in the rearwardly-directed yoke with the magnitude of the lever arm thereof being determined by the spacing between the horizontally-oriented pin through the pivot block and the orifice through the rearwardly-directed yoke for the fore-to-aft oriented pin, and (ii) moments in the fore-to-aft oriented pin and the plate attached to the hitch tube with the magnitude of the lever arm thereof being determined by the spacing between the horizontally-oriented pin through the pivot block and the hitch tube.        
Another Shortcoming of the Johnson Tow Bar
Of course, the various parts of the Johnson tow bar could be constructed much more massively to enhance the strength thereof in an attempt to more capably withstand the moments created internally within the tow bar due to the spaced-apart structuring of the yaw, pitch and roll axes. Unfortunately, such over-construction would defeat the ability to provide a relatively light-weight, easily manageable tow bar having the structure disclosed by Johnson.
Another such tow bar is disclosed in U.S. Pat. No. 5,765,851 issued Jun. 16, 1998 to Richard A. Parent. The Parent tow bar includes a forwardly-extending hitch member for connecting to a conventional receiver hitch fixedly connected to the rear of a towing vehicle. A pitch axis is defined by a horizontal transversely-oriented bolt, which connects a forwardly-directed yoke to the hitch member. A roll axis is defined by a fore-to-aft oriented bolt, which connects the forwardly-extending yoke to a rearwardly-extending yoke. A yaw axis is defined by a vertically-oriented bolt, which connects the rearwardly-directed yoke to the forward ends of a pair of towbar arms. The rear end of each towbar arm is connected to a towed vehicle.
As with the Johnson tow bar, one problem with the Parent tow bar is the plurality of moving parts thereof. Each of those moving parts is operatively subjected to substantial wear and abuse and therefore failure during use, namely, the horizontal transversely-oriented bolt, which is subjected to constant relative movement between the forwardly-directed yoke and the hitch member; the fore-to-aft oriented bolt, which is subjected to constant relative movement between the forwardly-directed yoke and the rearwardly-directed yoke; and the vertically-oriented bolt which is subjected to constant relative movement between the rearwardly-directed yoke and the towbar arms.
Also as with the Johnson tow bar, another problem with the Parent tow bar is the spaced-apart configuration of the various articulation axes thereof; more specifically, accommodation of pitch, roll and yaw movements between the towing vehicle and the towed vehicle are confined to separately-defined and spaced-apart axes: the horizontally-oriented pin through the hitch member and the forwardly-directed yoke for pitch movements, the fore-to-aft oriented pin through the forwardly-directed and rearwardly-directed yokes for roll movements, and the vertically-oriented pin through the rearwardly-directed yoke and the forward ends of the towbar arms for yaw movements.
As hereinbefore explained, the cause for concern in regard to the spaced-apart structuring of the articulation axes of the Parent tow bar arises from moments that are operatively created in the tow bar, which moments can only be countered internally within the tow bar by pitting one part thereof against another part thereof. Again, moments which must be countered internally within the tow bar by various parts of the tow bar increase wear and tear of those parts and, as a result, decrease the meantime before failure of the tow bar. In the structure of the Parent tow bar, the yaw axis is spaced rearwardly from the roll axis which, in turn, is spaced rearwardly from the pitch axis which, in turn, is spaced rearwardly from the receiver hitch of the towing vehicle.
Various force components are imposed by the towed vehicle on the vertically-oriented bolt through the rearwardly-directed yoke, the yaw axis, by virtue of the towed vehicle being connected to the vertically-oriented bolt by the towbar arms. For example, in any turning situation, the towed vehicle causes the towbar arms to exert a horizontal transverse force component on the vertically-oriented bolt through the rearwardly-directed yoke. Although the yaw axis at that vertically-oriented pin can accommodate transverse force components of the towed vehicle and the towbar arms, those transverse force components are imposed on the fore-to-aft oriented bolt through the rearwardly-directed and forwardly-directed yokes, and there is no other structure spaced forwardly therefrom that can provide another yaw axis to accommodate the transverse force components imposed on the fore-to-aft bolt through the rearwardly-directed and forwardly-directed yokes.
Similarly, in any operative situation where the towing vehicle enters an upgrade or a downgrade before the towed vehicle enters that grade change or the wheels of the towing vehicle are momentarily supported on a plane that is at a different elevation than the plane supporting the wheels of the towed vehicle, the towed vehicle causes the towbar arms to impose a vertical force component on the vertically-oriented bolt through the rearwardly-directed yoke of the Parent tow bar. Although the pitch axis at the horizontally-oriented bolt through the forwardly-directed yoke and the hitch member can accommodate such vertical force components imposed by the towed vehicle and the towbar arms, there is no other structure spaced forwardly therefrom that can provide another pitch axis to accommodate the vertical force components imposed on the horizontally-oriented bolt.
As a result of the foregoing, the moments which the Parent tow bar must internally oppose from force components imposed by the towed vehicle and the towbar arms can be described as follows:                (a) transverse force components create (i) moments in the rearwardly-directed yoke with the magnitude of the lever arm thereof being determined by the spacing between the vertically-oriented bolt through the rearwardly-directed yoke and the fore-to-aft oriented bolt through the rearwardly-directed and forwardly-directed yokes, (ii) moments in the forwardly-directed yoke with the magnitude of the lever arm thereof being determined by the spacing between the vertically-oriented bolt through the rearwardly-directed yoke and the horizontal pin through the forwardly-directed yoke, and (iii) moments in the hitch tube with the magnitude of the lever arm thereof being determined by the spacing between the vertically-oriented bolt through the rearwardly-directed yoke and the hitch member; and        (b) vertical force components create moments in the hitch member with the magnitude of the lever arm thereof being determined by the spacing between the horizontally-oriented bolt through the forwardly-directed yoke and the hitch member.        
Again, the various parts of the Parent tow bar could be constructed much more massively to enhance the strength thereof in an attempt to more capably withstand the moments created internally within that tow bar due to the spaced-apart structuring of the yaw, roll and pitch axes. And again, such over-construction would defeat the ability to provide a relatively light-weight, easily manageable tow bar having the structure disclosed by Parent.
A tow bar that has solved many of the problems of the Johnson and Parent tow bars is disclosed in U.S. Pat. No. 6,502,847 issued Jan. 7, 2003 to John Greaves. The Greaves tow bar includes a forwardly-extending hitching portion for connecting to a conventional receiver hitch fixedly connected to the rear of a towing vehicle. The equivalent of pitch, roll and yaw axes are all provided by a hitch ball member mounted in a hitch socket member with a rearwardly-directed hitch socket central aperture. The hitch ball member comprises two hemispheres, one spaced above the other in the hitch socket member. One of the hemispheres is fixedly attached to the forward end of one of the towbar arms, whereas the other hemisphere is fixedly attached to the forward end of the other towbar arm. The towbar arms extend rearwardly through the hitch socket central aperture. The hemispheres rotate relative to each other about a vertically-oriented axis when the towbar arms are spread apart to form a triangularly-shaped arrangement with the towed vehicle by use of two spaced-apart plate ball members fixedly connected to the rear ends of the towbar arms and connected to the front of the towed vehicle. Unfortunately, such relative rotation between the hemispheres, within the hitch socket member with the towbar arms fixedly attached thereto, reduces the remaining available spacing between the towbar arms and the periphery of the hitch socket central aperture thereby reducing the extent of relative movement available for accommodating pitch and yaw movements between the towing vehicle and the towed vehicle. Although special slots are provided in the hitch socket central aperture in order to enhance the movement available for relative yaw movements, a pitch movement occurring at the same time as a yaw movement that requires use of the special slots would defeat the intended purpose of the special slots.
An improvement provided by the Greaves tow bar over the Johnson and Parent tow bars is the substantial reduction in the number of moving parts that may be subject to failure during use. However, with one of the towbar arms being fixedly attached to a first one of the hemispheres and the other towbar arm being fixedly attached to the other hemisphere which is offset from the first hemisphere, an internal moment is operatively created between the two hemispheres.
Unfortunately, another drawback of the Greaves tow bar is the failure to provide a means for conveniently and rotatably storing the tow bar on the rear of the towing vehicle. Due to the towbar arms being fixedly connected to the hemispheres, due to the towbar arms extending rearwardly through the hitch socket central opening, and due to the limited ability to rotate the hemispheres thereby preventing the towbar arms from being displaced to an upright orientation, such convenient and rotatable storability does not appear to be possible without substantial structural modification to the Greaves tow bar, which is not taught or implied by the Greaves reference.
What is needed is a tow bar wherein the towbar arms thereof are not fixedly connected to hemispheres; wherein the towbar arms do not extend through a rearwardly-facing central opening in a manner that inhibits pitch and yaw movements between a towing vehicle and a towed vehicle; wherein the number of moving parts subject to failure during use is greatly reduced when a towed vehicle is being towed by a towing vehicle; wherein the connection between the towbar arms does not create a moment between the tow bar arms within a hitch socket member; and wherein the tow bar can be conveniently stored on the rear of a towing vehicle without having to disconnect the tow bar from the towing vehicle.